Addition agent for molten metals and process for making the same

ABSTRACT

An addition agent for adding an alkali metal or alkaline earth metal to a molten metal bath, for example for the addition of magnesium to a molten iron bath in the production of nodular cast iron in which the graphite is spheroidal in the as-cast condition, comprises briquettes of 5-50 percent by weight of the inoculant metal of a particle size 0.1 to 3 mm., 50-80 percent by weight of a porous material such as semi-coke, coke or graphite, having a particle size of 0.1 to 3 mm., and 10-25 percent by weight of a binder such as coal-tar pitch, coal-tar, or petrochemical pitch or bitumen. The inoculant metal and porous material are first admixed and then homogenized with the binder at a temperature of 80-130*C., after which briquetting is conducted. The briquettes are then heated from 150-250*C. for 15 to 90 minutes to harden them, and may be further heated for that period of time at 250-990*C. to bake them.

United States Patent Palumbo et al.

[ ADDITION AGENT FOR MOLTEN METALS AND PROCESS FOR MAKING THE SAME [76)inventors: Luigi Palumbo, via Eusebio Chini 22; Raffaele Tarozzi, viaMarangoni N. 1. both of Rome, Italy [22] Filed: June 20. 1974 [21] Appl.No.: 481,546

[30] Foreign Application Priority Data June 20. 1973 ital 50929/73 [52}US. Cl 75/130; 75/53; 252/475; 264/1 17 {51] Int. Cl.'-. C22C 33/08;B01] 23/02; CO9C 1/56 [58] Field of Search 75/53 130; 252/475. 476;264/1 17 {56] References Cited UNITED STATES PATENTS 2.881.068 4/1959Bergh 75/53 1656989 4/1972 Layland 75/130 R [451 Nov. 11, 1975 Fri/mmBummer-Peter D, Rosenberg Attorney. Agent. or Firm-Young A: ThompsonABSTRACT An addition agent for adding an alkali metal or alkaline earthmetal to a molten metal bath. for example for the addition of magnesiumto a molten iron bath in the production of nodular cast iron in whichthe graphite is spheroidal in the as-cast condition, comprisesbriquettes of 5-50 percent by weight of the inoculant metal of aparticle size 0.1 to 3 mm.. 50-80 percent by weight of a porous materialsuch as semicoke, coke or graphite having a particle size of 0.1 to 3mm., and l025 percent by weight of a binder such as coal-tar pitch,coal-tar. or petrochemical pitch or bitumen. The inoculant metal andporous material are first admixed and then homogenized with the binderat a temperature of 80130C.. after which briquetting is conducted. Thebriquettes are then heated from ISO-250C for 15 to 90 minutes to hardenthem. and 11121:" be further heated for that period of time at 250990Cto bake them 7 Claims, N0 Drawings ADDITION AGENT FOR MOLTEN METALS ANDPROCESS FOR MAKING THE SAME addition agents and processes, for theaddition in a conl0 trolled manner to a molten metallic bath, of metalswhich are relatively volatile and/or easily oxidized and- /or violentlyreactive with the metal bath.

For example, in the production of nodular cast iron, in which spheroidalgraphite is produced in the as-cast fonn by the inoculation of the bathwith small amounts of magnesium, a difficulty arises from the fact thatthe boiling point of magnesium is below the melting point of iron.Similar problems arise in steelmaking in connection with ladledesulfurization of the hot metal prior to refining.

In the past, a number of techniques and products for the inoculation ofbaths such as ferrous metal baths have been proposed, among them beingthe use of aporous support material as a vehicle for the inoculantmetal. Such a porous support has been for example coke, impregnated withthe desired metal in the molten state. Techniques for the production ofsuch additives are disclosed for example in Italian Pat. Nos. 743,720and 904,658, and comprise immersion of the porous material in the molteninoculant metal, followed by rapid cooling to solidify the metal whichhas penetrated the pores of the support.

However, such techniques and the resulting products have drawbacks byvirtue of the high reactivity and temperature of the inoculant metal.Thus, carbides form by the partial reaction of the metal with the carbonof the coke, and these carbides in the presence of moisture react toemit flammable gases. Moreover, the surface mechanical properties of thefinished product correspondingly deteriorate. If the cooling medium isoil, then this can ignite. The active metal can oxidize when the coolingmedium contains oxygen; and nitrides can form when the cooling mediumcontains nitrogen.

Accordingly, it is an object of the present invention to provide anaddition agent as defined above and a process for producing the same,which will overcome the foregoing difficulties and disadvantages.

Another object of the present invention is the provision of suchaddition agents which will be relatively simple and inexpensive toproduce and reliable in result when used, and to provide such processesfor the production thereof which will be easy to practice and dependablein result.

Briefly, the objects of the present invention are achieved by providingan addition agent and a process for producing the same, usable invarious pyrometallurgical operations such as hot metal desulfurizationand the nodularization of cast iron, in which particles of the reactivemetal and particles of a porous material are admixed with each other andthen with a binder, and then heated. The resulting product is uniformboth dimensionally and compositionally and is not subject to thedrawbacks and disadvantages recited above.

Further objects, features and advantages of the present invention willbecome apparent from a consideration of the following more detaileddescription of the invention.

ln greater detail, the invention comprises the formation of a mixtureconsisting essentially of particles of the active material and particlesof the porous support material which is then admixed with a binder,followed by briquetting of the mixture. The briquetted mixture is thenheated. Thereafter, if required, the briquettes are baked.

The composition by weight of the product can be as follows:

Metal S50% Porous material 50-80Z Binder l0-25k Homogenization andbriquetting of the mixture can be conducted between and 130C; Subsequentheating of the briquettes takes place between [50 and 250 C. and for atime between 15 and minutes. Baking of the briquettes, if carried out,can be performed at a temperature in a range of 250-900C. and for thesame time period.

The metal may be alkali metal or alkaline earth metal, or in general,any metal which is added to a molten metal bath and which has, relativeto the bath, great volatility and/or a high tendency toward oxidizationand/or violent reactivity with the bath. Examples are sodium, potassium,magnesium, calcium and strontium. The metal may be in the form of puremetal or an alloy thereof. The particle size is between 0.1 and 3 mm.

The bath itself may be any of the molten metal baths encountered inpyrometallurgy, and will ordinarily be ferrous, e.g., iron, nickel,cobalt or an alloy thereof.

The porous material may be semi-coke, coke, graphite, or any similarcompound or substance which has sufficient porosity and mechanicalstrength. The particle size may be 0.1 to 3 mm.

The binder may be coal tar pitch, coal tar, pitch or bitumen ofpetrochemical origin or mixtures of these in various proportions. Horn)genization with the mixed particles of the active metal and the porousmaterial is carried out for example in a masticator at a temperaturebetween 80 and C. but which ordinarily will not exceed by more than 50C.the softening temperature of the binder.

To enable those skilled in this art to practice the invention, thefollowing illustrative example is given:

A mixture is formed of 60 parts by weight of semicoke of particle sizefrom 0.3 to 1 mm. and 20 parts by weight of magnesium particles ofparticle size from 0.1 to 0.3 mm. it is admixed in a masticator with 20parts by weight of coal tar pitch having a softening point of 435C, at atemperature of 90C. for 10 minutes. The mixture thus obtained wasbriquetted in a press to obtain spherical briquettes 32 mm. in diameter.The briquettes were then hardened by exposure for 30 minutes in acurrent of air at 200C. with a flow rate of Nl/h. The hardenedbriquettes were then baked by exposure for 30 minutes in a current ofhydrogen having a temperature of 700C. and a flow rate of 150 Nl/h. Thebriquettes obtained showed the following properties at various stages:

Hardened briquettes l .03 I20 -continued Compressive Density Strengthgicm" kg Baked briquettes 93 300 The yield after baking is 90 percent.

The briquetted addition agent thus obtained is useful in ferrousmetallurgy as an addition agent for inoculating a bath of molten iron ina production of cast iron containing nodular or spheroidal graphite inthe as-cast condition.

From a consideration of the foregoing disclosure, therefore, it will beevident that all of the initially recited objects of the presentinvention have been achieved.

Although the present invention has been described and illustrated inconnection with preferred embodiments, it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit of the invvention, as those skilled in this art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the present invention as defined by theappended claims.

Having described our invention we claim:

I. An addition agent for the inoculation of a molten metal bath,consisting essentially of to 50 percent by weight of a metal selectedfrom the group consisting of alkali metal and alkaline earth metalhaving a particle size 0.l to 3 mm., 50 to 80 percent by weight of aporous material having a particle size of 0.1 to 3 mm., said porousmaterial being selected from the group consist- 4 ing of semi-coke, cokeand graphite, and l0 to 25 percent by weight of a binder which securessaid metal particles and said porous material particles together in abriquette.

2. An agent as claimed in claim 1, in which said selected metal ismagnesium.

3. An agent as claimed in claim 1, in which said binder is selected fromthe group consisting of coal tar, coal tar pitch, petrochemical pitchand petrochemical bitumen.

4. A method of producing an addition agent for inoculation of a moltenmetal bath, comprising admixing 5 to 50 parts by weight of a metalselected from the group consisting of alkali metal and alkaline earthmetal having a particle size of O.l to 3 mm., 50 to parts by weight of aporous mate rial having a particle size of 0. l to 3 mm., said porousmaterial being selected from the group consisting of semi-coke, coke andgraphite, and 10 to 25 parts by weight of a thermoplastic binder, at atemperature of 80 to C, briquetting the mixture to form solid bodiesthereof, and heating the briquettes at a temperature from about to about250C. for a time from about 15 minutes to about 90 minutes.

5. A process as claimed in claim 4, and further heating the briquettesat a temperature from about 250 to about 900C. for a time from about 15minutes to about 90 minutes.

6. A process as claimed in claim 4, in which said metal is magnesium.

7. A process as claimed in claim 4, in which said binder is selectedfrom the group consisting of coal tar, coal tar pitch, petrochemicalpitch and petrochemical bitumen.

1. AN ADDITION AGENT FOR THE INOCULATION OF A MOLTEN METAL BATH,CONSISTING ESSENTIALLY OF 5 TO 50 PERCENT BY WEIGHT OF A METAL SELECTEDFROM THE GROUP CONSISTING OF ALKALI METAL AND ALKALINE EARTH METALHAVING A PARTICLE SIZE 0.1 TO 3 MM., 50 TO 80 PERCENT BY WEIGHT OF APOROUS MATERIAL HAVING A PARTICLE SIZE OF 0.1 TO 3 MM., SAID POROUSMATERIAL BEING SELECTED FROM THE GROUP CONSISTING OF SEMI-COKE ANDGRAPHITE, AND 10 TO 25 PERCENT BY WEIGHT OF A BINDER WHICH SECURES SAIDMETAL PARTICLES AND SAID POROUS MATERIAL PARTICLES TOGETHER IN ABRIQUETTE.
 2. An agent as claimed in claim 1, in which said selectedmetal is magnesium.
 3. An agent as claimed in claim 1, in which saidbinder is selected from the group consisting of coal tar, coal tarpitch, petrochemical pitch and petrochemical bitumen.
 4. A method ofproducing an addition agent for inoculation of a molten metal bath,comprising admixing 5 to 50 parts by weight of a metal selected from thegroup consisting of alkali metal and alkaline earth metal having aparticle size of 0.1 to 3 mm., 50 to 80 parts by weight of a porousmaterial having a particle size of 0.1 to 3 mm., said porous materialbeing selected from the group consisting of semi-coke, coke andgraphite, and 10 to 25 parts by weight of a thermoplastic binder, at atemperature of 80* to 130*C., briquetting the mixture to form solidbodies thereof, and heating the briquettes at a temperature from about150* to about 250*C. for a time from about 15 minutes to about 90minutes.
 5. A process as claimed in claim 4, and further heating thebriquettes at a temperature from about 250* to about 900*C. for a timefrom about 15 minutes to about 90 minutes.
 6. A process as claimed inclaim 4, in which said metal is magnesium.
 7. A process as claimed inclaim 4, in which said binder is selected from the group consisting ofcoal tar, coal tar pitch, petrochemical pitch and petrochemical bitumen.